1. Field of the Invention
The present invention relates generally to the field of bearings and seals for such bearings. More particularly, the invention relates to a novel arrangement for maintaining lubricant, such as oil mist, within a bearing cavity, to keep contaminants out of the bearing cavity and also for simplifying the manner in which seals are integrated into a bearing structure.
2. Description of the Related Art
A wide variety of bearings are available and are currently in use throughout a range of industrial applications. Bearings are generally used to facilitate rotational movement in a mechanical application. Some bearings, known as guide bearings, are designed to facilitate linear motion. In general, a typical bearing includes a plurality of bearing elements situated in a housing. Depending upon the application and the anticipated loading, the bearing elements may be journal bearings, needle bearings, roller bearings, ball bearings, and so forth.
A journal bearing is typically formed from a plain cylindrical sleeve that carries a rotating shaft. Journal bearings are sometimes referred to as fluid film bearings because of the presence of a small film of lubricant used between the cylindrical sleeve and the rotating shaft. The coefficient of friction between the cylindrical sleeve and the rotating shaft is partially dependent on the whether a fluid film is fully developed. In essence, a fully developed fluid film creates a hydrodynamic pressure sufficient to float the shaft and its respective load relative to the sleeve or journal. The result of a fully developed fluid film is that there is essentially no physical contact between the rotating shaft and the bearing during operation. Proper development of a fluid film is, in turn, dependent on adequate lubrication of the bearing journal.
Adequate lubrication has other related and consequential benefits in addition to proper fluid film development. For example, it is commonplace to equip a bearing with a means for lubricating the bearing elements during operation to prolong the useful life of the bearings. This is typically accomplished by providing a synthetic or mineral grease or oil to coat the surfaces of the bearing elements. The application of grease or oil serves to preclude the ingress of contaminants, such as dirt, debris, moisture, and so forth into the bearing. In some applications the application of oil is accomplished by use of an oil ring. An oil ring hangs loosely over a shaft and rotates as the shaft rotates due to the ring""s contact with the shaft. Lubricant is carried from an oil sump to the shaft, then to the bearing liner. Another method is to use an oil circulating system wherein a pressurized lubricant is supplied directly to the bearing liner. In other applications, a pressurized oil mist may be circulated through a bearing cavity to provide continuous lubrication of the bearing. In addition to lubricating and cooling the bearing, each lubrication method operates to prevent the ingress of contaminants, while flushing the bearing cavity of contaminants and moisture.
One difficulty which arises in operation of typical fluid film bearings is proper isolation of the internal components of the bearing. Not only is it desirous to contain the lubricant in the bearing, it is also important to preclude contaminants, both liquid and solid, from entering the lubrication zone. This is generally accomplished through the use of an oil seal. A standard oil seal typically extends from a stationary member of the bearing assembly, such as a seal carrier or the bearing housing, to a moving surface of a shaft. The seal thus attempts to create coincidental surfaces which move relative to each other while providing a barrier against ingress of contaminants and egress of lubricants. Various oil seal designs have been employed to prevent communication between the internal components and the external environment. Much design work has been focused on the effectiveness and efficiency of such seals, particularly with respect to the manner of interaction of the seal with the shaft.
As stated previously, the purpose of a basic oil seal is to prevent contaminants from entering the internal components of the bearing while retaining the lubricants within the bearing housing. However, bearings operate in a variety of environments and quite often a standard seal does not provide adequate protection. For example, electrical machines generate a small pressure or vacuum within the motor frame due to rotation of the shaft and to air flow from an internal or external cooling fan. In such a case the vacuum tends to draw the lubricant from within the bearing housing out into the electrical machine and subsequently into the surrounding atmosphere. To combat this problem, a second seal, typically referred to as an air seal, may be disposed between the electrical machine and the oil seal. Thus the air seal serves to reduce or eliminate any effect on the pressure difference on the oil seal, while the oil seal performs its traditional service.
Still another special case arises where the bearing operates in a harsh environment. Such an environment may include fine airborne particles, liquid spray or perhaps exposure to various chemicals. It is often desirable to keep such contaminants out of the lubricant. Particles that enter into the lubricant may change the viscosity of the lubricant, or even degrade the lubricant itself, resulting in substandard performance and premature wear of the bearing. Introduction of certain chemicals into the lubrication system might wash away or degrade the fluid film causing a similar result. When a bearing is exposed to such an environment a secondary seal may be placed outside of the oil seal to provide greater protection. By way of example, a water baffle is sometimes placed on the exterior of a bearing housing to prevent fluids such as water from entering into the oil seal area.
Another difficulty with standard bearing oil seals is that when they fail, and thus require replacement, disassembly of the bearing and removal from the shaft is necessary to place the new seal in its proper location. The continuity of the seal (i.e. an annular member) is often desired to reduce the number of passages for ingress and egress to and from the internal components. Thus, with a continuous seal forming a ring, the seal must be slid over the end of the shaft before being placed in its proper position in the seal carrier or bearing housing.
There is a need, therefore, for an improved technique for sealing bearings which is effective at maintaining lubricant within the environment of the bearing, while also inhibiting the ingress of contamination and moisture into the vicinity of the bearing. There is also a particular need for a sealing technique for bearings which allows a single seal to operate in diverse environments thus replacing the use of multiple seals. In particular, there is a need for a sealing technique for bearings that can be both installed on new motors and other rotating equipment, as well as retrofitted to existing applications to obviate or reduce the need for multiple seal designs.
The invention provides a sealing technique designed to respond to these needs. In accordance with a first aspect of the technique, a seal system is provided for a bearing. The bearing includes a housing having two sides. The bearing also includes a bearing element disposed within the housing for facilitating motion of a rotating shaft. The seal system includes a seal carrier which may be integral with the housing or adapted to be mounted on the housing. The seal carrier has a groove in an inner periphery wherein a seal is disposed within the seal carrier groove. The seal has a soft flexible lip which contacts the rotating shaft. A groove is formed in an outer periphery of the seal for receiving a retaining device. The seal and the seal carrier are mountable on either side of the bearing even when the two sides experience dissimilar environments such as vacuum on one side and a liquid spray on the other. The technique also provides for splitting the seal and/or the seal carrier.
In accordance with another aspect of the technique, an alternative seal system for a bearing is provided. The bearing includes a housing having two sides. The bearing also includes a bearing element disposed within the housing for facilitating motion of a rotating shaft. The sealing system includes a first and a second seal carrier each housing an independent seal. The first seal carrier is mounted on the first side of the bearing with the first seal housed within the first seal carrier. The second seal carrier is mounted on the second side of the bearing with a second seal being housed within the second seal carrier. The first seal carrier and second seal carrier are substantially identical. Likewise, the first seal and second seal are substantially identical. While the seals are substantially identical, the first and second side of the bearing may be exposed to dissimilar environments. Again, the seals and/or the seal carriers may be split to facilitate installation and maintenance.
In accordance with yet another aspect of the technique a bearing is provided for facilitating movement of a rotating shaft. The bearing includes a housing having two sides. The bearing also includes a bearing element disposed within the housing for facilitating motion of a rotating shaft. The first side of the bearing includes a first seal carrier mounted to it with a first seal housed within the first seal carrier. The second side of the bearing includes a second seal carrier mounted on it with a second seal being housed within the second seal carrier. The first seal carrier and second seal carrier are substantially identical. Likewise, the first seal and second seal are substantially identical. The first and second side of the bearing may be exposed to dissimilar environments.
In accordance with a further aspect of the technique, a seal kit for a bearing is provided. The bearing includes a housing having a first and a second side. A bearing element is disposed within the housing for facilitating motion of a rotating shaft. The seal kit includes a seal having a soft flexible lip in contact with the rotating shaft. The seal also has a groove in an outer periphery of the seal for receiving a retaining member. At least one split may be formed in the seal, the split defining a pair of opposing and mating ends.